The search was for the messenger chemicals that activate pain receptors, but their discovery also has led to the development of two new drugs that don't affect the brain or central nervous system the way narcotics do, said Hargreaves, who was senior investigator on the study, which will be published April 26 in the Journal of Clinical Investigation.

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That potentially could provide an alternative form of relief from pain that at some point affects almost everybody, he said.

“The narcotics treat the symptoms of pain, but these treat the cause,” he said. When a person takes narcotics, the pain is still occurring, but the symptoms are no longer bothersome. The new drugs actually shut off the pain sensation where it's happening in the body, he said.

The health science center has patented the drugs, he said, and researchers are now working with pharmaceutical companies to set up clinical trials in human subjects.

Hargreaves compared the messenger chemicals to capsaicin, the substance that makes chiles hot.

Hot chiles make the mouth feel a burn because they activate receptors called transient potential vanilloid 1 (TRPV1). In many kinds of pain, including extreme heat and trauma, the same receptors are unlocked by chemical keys that Hargreaves described as natural capsaicins.

“What we've discovered is the body's natural key that turns on this lock,” he said.

The development of nonaddictive drugs to treat pain is important, Neugebauer said, but the scientifically exciting discovery is finding the messenger chemicals, which have been “quite an amazing puzzle” to pain researchers for some time.

Scientists had crafted various theories of how pain sensing TRPV1 receptors were activated in injured tissue, including whether heat altered the structure of the cell or created acidity in the tissues, he said.

The health science center researchers tested the new drugs on mice and rats with good results, Hargreaves said.

After giving the rodents repeated doses, he said, they didn't show any signs of addictive behavior the way they would with opiates.

As for the analgesic properties, he said, the animals were put through tests designed to allow the animal to end the experiment when the discomfort level gets too high.

First, inflammation similar to arthritis was induced in the animals’ tissue, he said. Then the rodents’ tender paws were stimulated.

“As soon as the animal withdraws its paw, the test stops,” he said. After the test animals were given the new drugs, they didn’t remove their paws until the stimuli reached normal intensity, he said.